Abstract
The measles virus (MeV), a member of the genus Morbillivirus, is an established pathogen of humans. A key feature of morbilliviruses is their ability to spread by virus–cell and cell–cell fusion. The latter process, which leads to syncytia formation in vitro and in vivo, is driven by the viral fusion (F) and haemagglutinin (H) glycoproteins. In this study, we demonstrate that MeV glycoproteins are sensitive to inhibition by bone marrow stromal antigen 2 (BST2/Tetherin/CD317) proteins. BST2 overexpression causes a large reduction in MeV syncytia expansion. Using quantitative cell–cell fusion assays, immunolabeling, and biochemistry we further demonstrate that ectopically expressed BST2 directly inhibits MeV cell–cell fusion. This restriction is mediated by the targeting of the MeV H glycoprotein, but not other MeV proteins. Using truncation mutants, we further establish that the C-terminal glycosyl-phosphatidylinositol (GPI) anchor of BST2 is required for the restriction of MeV replication in vitro and cell–cell fusion. By extending our study to the ruminant morbillivirus peste des petits ruminants virus (PPRV) and its natural host, sheep, we also confirm this is a broad and cross-species specific phenotype.
Highlights
As recently as 1980, the measles virus (MeV) killed 2,600,000 people per year, the effective use of a live attenuated vaccine has led to a significant drop in fatalities
To analyze MeV restriction by bone marrow stromal antigen 2 (BST2), a permissive cell line was generated as follows: The HEK293T cells were engineered to overexpress human SLAMF1 (293-hSLAM) using a standard lentivirus-based transduction system as described previously [21], with receptor expression being confirmed by flow cytometry. 293-hSLAMs, transfected with a FLAG-tagged pcDNA3.1-BST2 expression construct (Figure 1, pcDNA3.1-BST2/BST2) or pcDNA3.1 mock control plasmid (Figure 1, 3.1) for 24 h, were subsequently infected at high (2) multiplicity of infection (MOI)
Using green fluorescent protein (GFP) as a marker of viral replication and an Incucyte real-time plate imager to quantify fluorescence we identified a significant inhibition in MeV-GFP replication when BST2 was expressed in cells (Figure 1A)
Summary
As recently as 1980, the measles virus (MeV) killed 2,600,000 people per year, the effective use of a live attenuated vaccine has led to a significant drop in fatalities. The MeV is a small RNA virus, classified in the genus Morbillivirus, which encodes six transcription units and at least eight proteins. Two of these proteins, the fusion (F) and haemagglutinin (H) proteins, are glycoproteins, embedded as functional oligomers in the surface of the viral envelope [2]. SLAMF1 and nectin-4 are found on separate cells in vivo, immune and epithelial, respectively, contributing to a MeV life cycle that involves infection of both the lymphatic system and various epithelia [3]. One of the characteristic features of a MeV infection is the formation of syncytia, or multinucleated cells, both in vitro and in vivo, i.e., in the lymph node, thymus, and respiratory tract [4,5]. Morbilliviruses can spread by canonical particle formation (viral budding) and Viruses 2019, 11, 692; doi:10.3390/v11080692 www.mdpi.com/journal/viruses
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